In the production of integrated circuits, "chips" formed of silicon metal and on which are etched intricate circuits, are an essential component. The silicon wafers are carefully cut from a single crystal of silicon. These wafers are about 2" in diameter. In the processing of these wafers they become contaminated with dirt, dust, grease, etc. Before further processing into the final "chips" the wafers must be carefully cleaned.
In the semiconductor industry, wafers are rinsed in water after many process steps and, as indicated, then carefully cleaned and dried prior to the continuation of the fabrication process. At the present time, the silicon wafers are placed in a "boat" and dipped or sprayed with deionized water. The boats are subsequently loaded into a high speed centrifuge where the wafers are spin-dried. Recent technology has made use of vapor dryers utilizing isopropyl alcohol as a drying agent. The method creates a significant amount of waste over the period of a month, for example, and also a significant fire hazard.
It was desired, therefore, to develop a solvent system that was easily recovered and recycled, had excellent cleaning properties, had a convenient boiling point in the range of from about 40.degree. to 120.degree. C. and a very high, or no flash point. It was found that these criteria were met with a solvent composition which is a mixture of a fluorocarbon or chlorofluorocarbon, and a partially fluorinated alcohol. The system is unique especially for cleaning silicon wafers in that the acidic nature of the alcohol provides excellent cleaning, and the fluorocarbon or fluorochlorocarbon aids in drying the wafer without leaving any residue. The vapor may be recovered, condensed and reused.
The compositions hereof are used in the usual manner of rinsing in a boat or in a hot vapor system and then heating to a temperature sufficient to volatilize the solvent. Centrifuging may be used, but is unnecessary.
Reference may be had to Japanese Kokais Nos. 61/255977 and 58/122980. The former thermally stabilizes a working medium including a hydrocarbon (e.g., methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane or n-heptane,) alcohol, e.g., methanol, ethanol, 2,2,2-trifluoroethanol or 2,2,2,3,3-pentafluoropropanol, a mixture of fluorinated alcohol and water or ammonia, 4-8C perfluoroalkane, or freon, an azeotropic mixture of CCl.sub.2 F.sub.2 and CHF.sub.2 --CH.sub.3 or azeotropic mixture of CHClF.sub.2 and CClF.sub.2 CF.sub.3. To the working medium is added phosphine sulfide and glycidyl ether and optionally lubricating oil. This composition is used to treat steel, aluminum, aluminum alloy, or brass.
The latter Japanese Kokai teaches a processing fluid for use in a heat transfer device of a closed fluid cycling system with evaporation and condensing sections. The processing fluid is composed of trifluoroethanol and contains up to a maximum of 15% water. The fluid used contains water, ethanol, freon, mercury, cesium, pentane and heptane.
Each of these compositions is used for a different purpose and in a different manner.